France

France uses a set of measures before 1795 that had many characteristics of Imperial units, but these random units lack any unified system of measurement. Charlemagne and successive kings try but fail to impose a unified system of measurement in France. In England, by contrast, the Magna Carta decrees that there shall be one unit of measure throughout the realm. The names and relationships of many units of measure are adopted from Roman units of measure and many more are added. France has an estimated seven or eight hundred different names for the various units of measure before 1795. Making matters even worse, the quantity of each unit of measure differs from town to town and even from trade to trade to such an extent that the lieue (league) could vary from 3.268 km in Beauce to 5.849 km in Provence. An estimated quarter of a million different units of measure are in use in France on the eve of the Revolution. Although certain standards, such as the pied du roi (foot of the king) have a degree of pre-eminence, many traders use their own measuring devices, giving scope for fraud and hindering commerce and industry. There is a wish that the units of measure should be for all people and for all time and therefore not dependent on an artifact owned by any one particular nation.

Tallyrand, at the prompting of the savant Condorcet, approaches the British and the Americans in the early 1790s with proposals of a joint effort to define the metre. In the end, these approaches come to nothing and France decides to go it alone.

The French Revolution is an influential period of social and political upheaval in France that lasts from 1789 until 1799 CE. The Revolution overthrows the monarchy and establishes a republic. The Revolution profoundly alters the course of modern history, triggering the decline of theocracies and absolute monarchies. Historians widely regard the Revolution as one of the most important events in human history. The French Revolutionary government in 1795 CE gives the metric system a legal basis.

Metric Pioneer Antoine Lavoisier (1743–1794 CE) Father of Modern Chemistry helps construct the metric system during the French Revolution while working alongside Benjamin Franklin in France.

The French (during the early part of the twentieth century) introduce their own units of power – the poncelet, which is defined as being the power required to raise a mass of 100 kg against standard gravity with a velocity of 1 m/s giving a value of 980.665 W. However, many other European countries define their units of power (the Pferdestärke in Germany, the paardekracht in the Netherlands and the cavallo vapore in Italy) using 75 kg rather than 100 kg, which gives a value of 735.49875 W. Eventually, the poncelet is replaced with the cheval vapeur, which is identical to equivalent units of measure in neighboring countries.

The eleventh CGPM (Conférence Générale des Poids et Mesures / General Conference on Weights and Measures) in 1960 faces the question of what to call a new reorganization and extension of measures. The name Metric System had referred to the units for length and mass. What the CGPM had created was much more comprehensive, and after some discussion, this new system was called the International System of units or SI after its French initials. For the first time, the world had not merely universal units, but a universal system of units. In 1977, these units, along with the stere and the livre (and amongst others, the German pfund) were proscribed by EEC Directive 71/354/EEC which requires EU member states to standardize on the International System of Units (SI).